Product Application of Schottky Diode

Product Application of Schottky Diode.
We often use Schottky diodes in switching power supplies, but the performance varies greatly from manufacturer to manufacturer. When we choose Schottky, we must consider the following parameters:
1. Conduction voltage drop VF.
When the VF is the positive guide of the diode, the voltage drop at both ends of the diode, the greater the current through the diode, the greater the VF; when the temperature of the diode is higher, the VF is smaller.
2. Reverse saturated leakage current IR.
IR refers to the current flowing through the diode when the reverse voltage is added at both ends of the diode, and the reverse leakage current of the Schottky diode is larger. The Schottky diode is chosen as far as possible to choose the diode with low IR.
3. Rated current IF.
Refers to the average current value calculated according to the allowable temperature rise during the long-term operation of the diode.
4. Maximum surge current IFSM.
Excess forward current that is allowed to flow. It is not a normal current, but an instantaneous current, which is quite large.
5. Maximum peak reverse voltage VRM.
Even if there is no reverse current, as long as the reverse voltage is continuously increased, the diode will be damaged sooner or later. The reverse voltage that can be added is not the instantaneous voltage, but the forward and backward voltage added repeatedly. Since AC voltage is applied to the rectifier, its maximum value is a specified important factor. Maximum peak reverse voltage VRM refers to the maximum reverse voltage that can be applied to avoid breakdown. At present, Schottky has the highest VRM value of 150V.
6. Maximum DC reverse voltage VR.
The maximum reverse peak voltage mentioned above is the peak voltage added repeatedly, and VR is the value when the DC voltage is continuously applied. For DC circuits, the maximum DC reverse voltage is important for determining allowable and upper limit values.
7. Maximum operating frequency fM.
Due to the existence of the junction capacitance of the PN junction, when the operating frequency exceeds a certain value, its unidirectional conductivity will become worse. The FM value of Schottky diode is high, and the maximum value can reach 100GHz.
8. Reverse recovery time Trr.
When the working voltage changes from the forward voltage to the reverse voltage, the ideal situation for the diode to work is that the current can be cut off instantly. In fact, it usually takes a little time to delay. The amount that determines the current cutoff delay is the reverse recovery time. Although it directly affects the switching speed of the diode, it does not necessarily mean that the value is small. That is, when the diode is suddenly reversed by turn-on, the reverse current decays greatly to close to the IR. This index is very important when the high-power switch diodee works in the high-frequency switching state.
9. Maximum dissipative power P.
If there is a current flowing through the diode, it will absorb heat and raise its own temperature. In practice, the external heat dissipation also has a great influence on P. Specifically, the voltage added to both ends of the diode multiplied by the current flowing through plus the reverse recovery loss.
Comparison between Schottky and fast recovery diodes.
Fast recovery diodes are diodes with very short reverse recovery time (below 5us), and their forward voltage drop is higher than that of ordinary diodes (0.8V 2V). The reverse voltage is less than 1200V, and the performance can be divided into fast recovery and ultra-fast recovery, and the latter can reach less than 100ns.
Schottky diode reverse recovery time is below 10ns, reverse leakage current is large, voltage resistance is low, generally less than 150V is mostly used in low voltage applications.
The difference between Schottky diodes and fast recovery diodes: the recovery time of the former is about 100 times shorter than that of the latter, and the reverse recovery time of the former is about a few nanoseconds. The former has the advantages of low power consumption, high current and ultra-high speed, while the latter has higher switching speed, higher voltage withstand and low reverse leakage, so it can be used in situations with high voltage and high frequency.
In addition, the ESD tolerance of Schottky diodes is lower than that of fast recovery diodes.